1. Field of the Invention
The present invention relates to image processing, and relates more particularly to high definition video image rescaling.
2. Description of the Background Art
Rescaling video images is an important aspect of many types of video and multimedia applications, and therefore efficient video resealing is a significant consideration of designers and manufacturers of image processing systems. A digital video image may be described as a grid of values that are samples of a continuous two-dimensional function. The value of each pixel of the video image represents the value of the continuous function at a point in the center of the pixel. A large video image typically includes a greater number of pixels, or samples, than a small video image. A large video image may. be reduced by decreasing the number of pixels, and a small video image may be magnified by increasing the number of pixels.
In video image resealing, a rescaled image typically includes destination pixels that are derived from source pixels of a source image. The contribution each source pixel makes to each destination pixel is determined by applying a filter function to each source pixel. Various types of filter functions may be used for video resealing. A filter function is typically centered on each source pixel and scaled to the value of the source pixel. The scaled filter functions are summed together to produce a reconstructed function for the source image. The reconstructed function is then sampled appropriately to produce the required number of destination pixels. A magnified image includes a greater number of pixels than the source image, and a reduced image includes a smaller number of pixels than the source image.
The operation of summing together the scaled filter functions may be computationally intense, requiring significant amounts of processing power and time. Some filter functions may produce high quality rescaled images, but have a very high cost in terms of system resources. Other filter functions may require fewer system resources, but produce lower quality rescaled images. Therefore, selecting an optimum filter function for efficient and effective video rescaling is a significant consideration of designers and manufacturers of image processing systems.
In accordance with the present invention, a system and method are disclosed for high definition video rescaling. In one embodiment, a set of source pixels is provided, each source pixel having an associated amplitude. A set of destination pixel locations is determined based on a resealing factor. A magnified image includes a greater number of pixels than the source image, and a reduced image includes a smaller number of pixels than the source image.
A normalized filter function is centered on each source pixel and scaled to the amplitude of the source pixel. The normalized filter function is the same for each source pixel. The filter functions for the source pixels are summed together to produce a reconstructed function. The reconstructed function is sampled at the destination pixel locations. The amplitude of the reconstructed function at the destination pixel locations is the amplitude of the destination pixel. The destination pixels are then incorporated into a rescaled image.
In the preferred embodiment of the present invention the filter function is a sinc product function. The sinc product function is a first sinc function having a first period multiplied by a second sinc function having a second period that is an odd integer multiple of the first period, so that the sinc product function has a smaller amplitude than a sinc function as the function converges to zero.